The plant cell wall is a complex structure consisting of different polysaccharides, the major components being cellulose, hemicelluloses and pectins. The resistance of the plant cell wall to digestion presents significant challenges in the animal production industry. Presently, in livestock agriculture while a high-forage diet is desirable, it does not currently satisfy the demands of modern animal production. Fiber digestion is a limiting factor to dairy herd milk yield and composition, and to beef production in beef operations feeding a high forage diet, and hence restricts profitability of farmers. Enhancing fiber digestion has a dual impact: 1) the animal eats more due to a reduced gut fill and therefore produces more, and 2) the animal gets more out of what it eats since the fiber is more digestible. Ultimately, this should increase milk yield, in dairy cows, and beef production in forage fed animals. Farmers either have to put up with a lower level of feed digestibility and hence productivity, or they can use inoculants, forage additives or other amendments that improve the digestibility of feed.
Accordingly, farmers can treat ensiled feed or other animal feed with fiber degrading enzymes, originating mainly from molds, to improve digestibility of feed. In addition, there are several commercially available Saccharomyces cerevisiae yeast strains that when fed to cattle reportedly improve fiber digestion (Erasmus et al., (1992) J. Dairy Sci. 75: 3056-3065; and Wohlt et al., (1998) J. Dairy Sci. 81: 1345-1352). Plant tissues and fibers can be disrupted to help release nutrients by adding organisms or enzymes produced by these organisms to forage before feeding or ensiling.
For example, in U.S. Pat. No. 6,037,161, an Aspergillus acetyl esterase nucleic acid sequence is described which encodes an enzyme with activity towards acetylated xylans that may be used to modify plant materials for enhanced nutrient availability. However, these methods can be difficult and expensive to practice because recombinant technologies, fermentations, and chromatographic processes are required. In addition, the resultant enzyme has a narrow range of substrates and can fail to effectively release nutrients from many plant materials.
Generally, for an animal to make efficient use of the feed it consumes, the energy demands of the microorganisms in the digestive tract must be met and synchronized with the availability of plant proteins. A lack of synchrony will lead to a) proteins and other nutrients being poorly utilized in the digestive tract, b) a loss of nitrogen, in urine and feces and c) a need to feed excessive amounts of protein concentrates as supplements to the diet. The use of organisms and enzymes can improve or enhance the value of the feed animals receive and the performance of the animals. For example, WO 92/10945 discloses such a combination for use in enhancing the value of prepared silage. WO 93/13786 and WO 96/17525 relate to the enhancement of animal performance using microorganisms, while WO 93/13786 refers to a species of Lactobacillus. 
Silage can be spoiled when aerobic organisms, such as some yeast and molds, propagate in the stored feed. For example, silage can be damaged by air leaks in a silo or when air is introduced while farmers are removing part of the silage. In the presence of oxygen, yeasts, molds, and aerobic bacteria can consume nutrients, and release unpleasant or toxic metabolites. This elevated aerobic microbe activity has been considered undesirable since it often results in aerobic spoilage of silage and the consequent depletion of silage dry matter (DM) nutrition. However, some microbes, such as killer yeast (see U.S. Pat. No. 6,489,158) and Lactobacillus buchneri strains (see U.S. Pat. No. 6,326,037) can beneficially inhibit growth of spoilage microbes thereby stabilizing nutrient value of ensiled plant materials. A further method to reduce this problem is to inoculate the silage with a fast growing microbe, such as Lactobacillus species, which release organic acids to lower the silage pH and inhibit growth of spoilage organisms.